Have you checked your servlet logs to see if the UnavailableException errors
actually are being thrown? You don't say what version of Tomcat you are using,
but (if I remember correctly) version 3.1 did not actually honor
UnavailableExceptions thrown from init().
Craig McClanahan
Tom O'Connor wrote:
> In the init() method of my Servlet class, I populate 2 String instance
> variables that are later used in the doPost() method. The String values are
> populated by calling .getInitParameter() on the ServletConfig instance
> passed into init(). I verify that the String returned from
> .getInitParameter() != null inside init().
>
> After tomcat starts, I start a client program that generates HTTP requests
> aimed at the servlet. More often than not, these requests fail with 500
> Server Error as the response. For each failed request, in
> $TOMCAT_HOME/logs/tomcat.log there is a
> NullPointerException and a stack trace, and the stack trace points me to a
> line in my servlet where I invoke a method on the String instance variables
> that should have been initialized in init().
>
> This is *NOT* a configuration file issue. I can say this because in the
> same webapp, I have 2 servlets that each have the same servlet-class element
> in web.xml. The first servlet will generate failures (sometimes) but the
> second servlet (which is the same class, but a different instance) will
> succeed. The only thing different between the two instances are the
> init-param values in web.xml. I also swap which servlet I invoke first and
> it's the first servlet invoked that fails.
>
> I've tried this using both Apache+mod_jk over Ajp13, and invoking the
> servlet directly through Tomcat's HTTP adapter.
>
> Doesn't the servlet spec say that no thread shall enter Servlet.service()
> until Servlet.init() has successfully completed? If that's true, how can my
> instance variables be null?
>
> The servlet looks like this:
>
> public class S extends HttpServlet {
> private String n = null;
> private String v = null;
> public void init(ServletConfig config) throws ... {
> super.init(config);
> n = config.getInitParameter("n");
> v = config.getInitParameter("v");
> if (n == null) throw new UnavailableException();
> if (v == null) throw new UnavailableException();
> // snip
> }
> public void doPost(...) throws ... {
> // this.n and this.v are used in here
> }
> }
